The respiratory muscles are a major determinant of thoracic cavity shape and thus the distribution of regional ventilation. Respiratory insufficiency is the usual cause of death in many primary neuromuscular disorders. Respiratory muscle fatigue is believed to be a major factor in hypercarbic respiratory failure associated with lung or cardiovascular diseases or both. A recent NHLBI workshop summarized the difficulty of studying respiratory muscle fatigue because of our limited understanding of the relationships between tension developed by the respiratory muscles and pressures which expand the thoracic cavity and other parameters which can be measured in intact animals or man. This project utilizes a new video roentgenographic technique to determine the regional shape, displacements and muscle shortening of the diaphragm and ribcage to elucidate the basic mechanics of the diaphragm and ribcage. By comparing muscle shortening and curvature of the diaphragm in intact animals under conditions in which the transdiaphragmatic pressure and muscle tension can be measured, the relationship between muscle tension and pressures can be determined. The detailed three dimensional anatomic data provided by this methodology coupled with more conventional physiologic measurements should answer important questions posed by previous studies of the coupling of the diaphragm abdomen and ribcage. The range of motions possible for individual ribs will be determined and related to the chest wall shapes produced by variations of rib .motions. These studies of the kinematics of the ribcage can be used to compute the mechanical advantage of the ribcage musculature.